We must pursue all political avenues for saving lives. Yet this investment in diplomacy should not eliminate more significant kinds of intervention. Without greater pressure, the Syrian regime is unlikely to consent to a transitional government, or even decelerate its killing of its own people.

The reason that the Assad regime is able to continue its crimes is simple: it can get away with it.

The United States has not taken serious steps to show otherwise. A strategy focused on sanctions, diplomacy, and rhetoric has not deterred Assad's onslaught. On the contrary, declaring and then abandoning red lines only emboldened it.

Supporting rebels with "non-lethal aid," recently upgraded to "light arms," and even shipments of cash, remains insufficient against a state's war arsenal - backed up with blank checks from Iran and Russia.

Assad enjoys a huge power advantage over the forces that oppose him. To reduce the regime's willingness or capacity to kill, international players must narrow that gap.

President Obama backed away from direct military intervention. A range of options existed, from striking Syrian Air Force runways to the establishment of a no-fly zone. Such actions could have reduced Assad's capacity to brutalize his population or altered his calculation of the costs and benefits of doing so.

Short of direct military intervention, the U.S. should go to the fullest possible lengths to persuade Assad's foreign backers to stop enabling him militarily, politically, and financially. This means using every form of diplomatic leverage with Russia, Iran, and Iraq. The U.S. can also deliver more serious military aid to the rebellion via our contacts in the Free Syrian Army.

Arguments circulate against increasing U.S. involvement in Syria. Here are 12 common ones, and why they fall short.

1. The opposition is too fragmented.

This argument mixes cause and effect. A grassroots movement for freedom and dignity showed admirable unity when it first braved bullets and went into the streets in spring 2011. After months of repression and no meaningful international support, the movement militarized and splintering increased. A main cause of fragmentation among rebels is competition among their foreign patrons. Greater coordination among external supporters of the revolution is key for building unity within it. This is where clearer American leadership can make a difference.

2. Arms might wind up in the hands of Islamist extremists.

Jihadist groups became powerful in Syria because blood flowed for months while the opposition's cries for assistance went ignored. Had the international community acted earlier, these extremists might never have emerged on the scene. Most Syrians view al-Qaeda as another form of tyranny. Many have risked their lives to protest agianst it. It is a cruel irony that the United States, which championed the "war on terror," now leaves besieged civilians to fight al-Qaeda on their own.

3. Greater involvement would make Syria another Iraq or Afghanistan.

In Iraq and Afghanistan, the U.S. imposed regime change from the outside. In Syria, an anti-regime struggle emerged from the grassroots. The choice facing America is not about starting a war but about abandoning a population whose state makes war against it. Besides, even Syrian oppositionists who pleaded for a U.S. strike insist that they do not want American boots on Syrian soil.

4. Assad is better than the alternatives.

If Assad is, as most of the world is convinced, a despot willing to destroy his country to stay in power, then he is a war criminal. If, as supporters insist, he is protecting his country from terrorism, then he is a failure. Few countries have suffered more terrorism than Syria. Assad bears responsibility for the incalculable ruin occurring under his tenure.

There is no shortage of talent ready to lead a free Syria. Shows of leadership occur on the ground everyday as citizens come together to feed, govern, heal, and care for their communities, even under daily shelling and siege. Their civic work is what keeps families, and indeed the revolution, alive. It would make any democracy proud.

5. If Assad falls, there will be chaos.

The Assad regime is the primary cause of chaos in Syria. It has taken deliberate steps to sow chaos, from purposefully strengthening Jihadists (so it can then claim to fight them) to unleashing loyalist militias to beat, rape, and steal.

Syria has been subjugated to repressive family-rule for more than 40 years. No one claims that it will become a stable democracy over night. Still, in initiatives such as The Day After Project, Syrians are anticipating the challenges of transition and outlining specific plans to address them.

6. U.S. intervention will provoke stronger involvement by Russia and Iran, leading to dangerous escalation.

The logic of intervention -- to show that there are repercussions for state brutality -- applies to Assad's foreign backers as much as to Assad himself. The U.S. has three options: (1) negotiate boldly with Russia and Iran, offering shows of concern for their other vital interests in exchange for change in their policies toward Syria; (2) confront their support for Assad with its own stronger support for the rebellion; or (3) sit back as Russia and Iran do whatever they wish. The uncertainty surrounding the first two options must be weighed against the certain tragedy of the third: the Syrian regime will continue to kill more civilians every day.

7. Intervention will only intensify violence.

The regime is responsible for the vast majority of devastation in Syria, as well as the environment of death and impoverishment in which other agents of extremism flourish. The Syrian state has hugely better capabilities than the opposition. It has a willingness to kill that is unhindered by a sense of the costs for doing so. As long as Assad has this capacity and does not face serious disincentives, he is likely to continue to commit atrocities. This is what stronger international intervention must aim to change.

8. It's too risky.

Greater involvement carries risks. But so does sitting on the sidelines. The policy of Western inaction is the context in which dangerous extremists have expanded their presence in Syria. What will happen when foreign Jihadists return home to Europe, Jordan, North Africa, or elsewhere? How long will it be until those enraged by the slaughter of Syrians commit terrorism against the U.S.?

9. It's too late.

Intervention would have been better two years ago than now. It is better now than later.

10. Intervention is not a panacea.

That's true, but neither is any other possible course of action. "Panacea" is an unhelpful, unrealistic standard against which to judge available policy options. What is certain is that the option least likely to end the Syrian nightmare is continuation of the Syrian nightmare.

11. U.S. militarism is not to be trusted

From the left, some criticize U.S. intervention as neo-imperialist militarism that will advance American hegemony rather than aid the oppressed. This criticism is important, but should not justify inaction that effectively forsakes the oppressed. Non-interventionists can direct their activism toward ensuring that US involvement does not stray from humanitarian goals and remains within the parameters for which Syrian revolutionaries are themselves clamoring.

12. America has no interests in Syria.

The U.S. has at least three interests in Syria. First, it wants stability in the Middle East. From bombs in Lebanon to a refugee crisis in all of Syria's neighbors, continuation of the Syrian conflict threatens the region as a whole.

Second, the U.S.'s current policy undermines its credibility. The US claims to champion freedom and human rights. Its hands-off stance on Syria suggests that those principles only apply when they provide cover for economic or other benefit.

Third, our most important interest is - or should be - ethical. We have material and political strength to aid those who lack means to protect themselves from ruthless oppression. We have a duty not to back down in the face of atrocities.

Thus far, a sense of moral obligation and common humanity has been insufficient to rouse Americans to support greater involvement in Syria. And so, every day, Syrian children are struck dead, have limbs blown off, shiver in freezing refugee camps, or starve. Bombs fall from the sky, political prisoners become skeletons, and families survive on boiled grass. World heritage sites turn to rubble and polio spreads.

Politicians tell us that America is the greatest nation on earth. If so, there is much more that we can do to stop the tragedy in Syria. If we do not, we share responsibility for it.